Detached garage feeder gauge

[fizzog]

Hi,
I am planning to run a 4 wire feeder out to my detached garage (shared neutral). I'm looking to have 4 circuits in the garage. 1x20A for about 8 receptacles, 1x15A for lighting, 1x15A for garage door openers and 1x15A for outside driveway lighting. Thinking of using a DP 30A breaker at the main house panel. Sub-panel in garage will have a disconnect and grounding rods (2).
Question: am i OK running 8 gauge copper or do i have to use 6 ga?
My garage is about 100 ft from the house and the internal run through the hose from the main panel is about 60-70 ft. So total length about 170 ft.
Thanks in anticipation.

Jim.

Edit: should have said. Will only be using hand tools, no welders or similar and lighting of course.

 

[Aceman]

My voltage drop app says #6 copper for a 30 amp load at 170'.

If you end up running the #6, I would just install a 50 amp breaker in your main panel and then buy a main lug panel for your garage and backfeed a 2 pole 50 with a retainer kit. This backfed breaker is your main.

Or you can buy a 100 amp main breaker panel and use that instead. Most lugs will go down to #6 wire, but check before you wire it.

 

[justsam]

You do not need a main breaker if you are under 6 circuits in the garage. For convenience I would put one in since the cost is just not that much more.

Are you sure you will not have other loads such as compressor welder, etc?

 

[wyliesdiesels]

Not sure what u mean by shared neutral.....the #6 Aceman suggested will have a 3.4% voltage drop @ max load of 50a so u should be fine with that!

The ground wire would normally be #10 but since you oversized the wire to compensate for voltage drop, the ground wire should be minimum #8.

If u think u will ever have bigger tools or an air compressor, u may just want to go bigger on the feeder....

 

[fizzog]

Not sure what u mean by shared neutral.....the #6 Aceman suggested will have a 3.4% voltage drop @ max load of 50a so u should be fine with that!

The ground wire would normally be #10 but since you oversized the wire to compensate for voltage drop, the ground wire should be minimum #8.

If u think u will ever have bigger tools or an air compressor, u may just want to go bigger on the feeder....

By that I meant a multi-wire circuit. 2 lives, 1 shared neutral, 1 ground.
Thanks all for the replies. I was hoping to not have to wrestle with #6. I was hoping that the shared neutral circuits would effectively give me 240V and therefore allow me to use the thinner gauge due to the reduced voltage drop.

 

[pattenp]

Use can use #8 Cu for 170 feet but the VD will be 3.3% @ 30 amps, which is border line okay. But the feed should be sized based on the total loads(100% non-continuous + 125% continuous). So as long as your calculated total load is at 30 amps or less, then using #8 Cu will do. But it always seems if you do just enough, later you'll wish you did more.

 

[fizzog]

But it always seems if you do just enough, later you'll wish you did more.

True enough! I guess while i'm digging a trench and all i may as well go with #6.
Thanks again all.

 

[wyliesdiesels]

By that I meant a multi-wire circuit. 2 lives, 1 shared neutral, 1 ground.
Thanks all for the replies. I was hoping to not have to wrestle with #6. I was hoping that the shared neutral circuits would effectively give me 240V and therefore allow me to use the thinner gauge due to the reduced voltage drop.

Yeah thats what I thought u meant but u had already said 4-wire feed which is the same thing as a multi-wire circuit....the shared neutral has nothing to do with alleviating voltage drop. The vd calcs i did were for 240v. The issue u have is distance.

 

[Falcon67]

After pricing 4x170' of Cu, might consider MHF 2-2-2-4 at under $2/ft most places. Overkill, but thinking total cost.

 

[pattenp]

Glad to see you suggest the MHF. There are a couple of treads where Cu vs. Al is discussed. I just didn't feel like going there again in the tread.

After pricing 4x170' of Cu, might consider MHF 2-2-2-4 at under $2/ft most places. Overkill, but thinking total cost.

 

[Falcon67]

Glad to see you suggest the MHF. There are a couple of treads where Cu vs. Al is discussed. I just didn't feel like going there again in the tread.

LOL. Run 2" Schedule 80 conduit and then he could run air AND power with one install.